The present invention relates to an interactive and branched cable network adapted to be connected to a group of apparatuses capable of receiving and transmitting information, which apparatuses each comprise a modulator-demodulator arrangement, said group of apparatuses being connected to a central distributor provided with at least one head-end modulator-demodulator arrangement, the modulators-demodulators operating in a first frequency range in the case of transmission and in a second frequency range in the case of reception, each of said two frequency ranges being divided into a plurality of sub-ranges each using a different frequency.
Such a network is used, for example, for transmitting television or radio programs to users, enabling the transmission and treatment of "ascending" or upstream digital data coming from subscribers for the head of the network.
One of the key points of such a system is the development of specific bidirectional modulator-demodulator arrangements and the invention thus also relates to a modulator-demodulator arrangement for such an interactive and branched cable network.
A network of the type described in the opening paragraph is known from the article by K. Prasad: "Design of "Transnet" a special local area network", IEEE 11th conference on Local Computer Networks, 6th-8th Oct., 1986; IEEE New York US; pages 46-55. According to this document a branched network (cf FIG. 1 of this document) is used for different applications ("TV, data communications, voice systems" cf page 51 of this document). There is a frequency range for output channels ("outbound") and another frequency range for input channels ("inbound"), each information path taking up a specific sub-range (referred to as "channel" in the document). All information is transmitted via a common physical channel whose bandwidth is 30-400 MHz (cf FIG. 2b of the document), and must thus be selected at the level at which each information is used.
Because of the wide band of the common physical channel, the noise is considerable and the ascending information components are very difficult to demodulate correctly, particularly because the ascending or upstream paths are more polluted by the noise than the descending or downstream paths, for the network forms an antenna and a collector of all kinds of noise in this case.